In C-band microwave communications, electromagnetic energy is typically collected and focused using a parabolic reflector into an opening for a circular wave guide positioned near the focal point of the reflector. This circular wave guide is mounted through an opening in the center of a scalar ring. A scalar ring is an integrally formed circular metal plate with multiple concentric "ribs" coaxial with the opening of the plate. It is typically supported above the reflector using some sort of tripod mount. The circular wave guide is secured to the scalar ring with set screws through a sleeve integrally formed with the plate. The back end of the circular wave guide is coupled to a rectangular wave guide for mating with a low-noise block down-converter unit that transforms and down-converts the frequency of the microwave signal to an IF signal for transmission to a receiver unit.
The reflector tends to accumulate electric charge due to atmospheric ionization. Since there is a ground path through the wave guide and low-noise block down-converter to the receiver, the accumulation of sufficient charge may sometimes cause damage to circuitry in the low-noise down-converter when it is discharged or when it raises the potential of the feedhorn significantly above ground.
Prior art solutions to the problem have involved placing an electrically insulating gasket between the wave guide portion of the low noise converter unit and the wave guide. Insertion of an insulator in that position, however, substantially interferes with the propagation of the microwave down the wave guide and thus seriously compromises performance of the antenna system.